Multiple sclerosis (MS), like many other autoimmune diseases, is influenced by genetics, hormones, and the environment. More than 2.5 million people are afflicted worldwide. Women are affected two to three times more than men. There is no cure. The generation of functional regulatory T cells (Tregs) in vivo is a major goal for the treatment of immune-mediated diseases including MS. A better understanding of how Tregs are controlled will benefit the development of new therapeutics. The transcription factor aryl hydrocarbon receptor (AhR) has the potential to promote the differentiation of immunosuppressive Tregs. Hence, AhR-induced Treg differentiation has emerged as a potential therapeutic target to treat autoimmune disease. Our preliminary data suggest exacerbation of AhR-induced Treg differentiation in females and a novel role for ER-AhR crosstalk in the immune system. We further demonstrate a sex-biased role for tumor necrosis factor receptor type 2 (TNFR2) in the regulating experimental autoimmune encephalomyelitis (EAE), a prototypical animal model for MS. Lastly, we show regulation of TNFR2 expression on Tregs by AhR. The overall goal of this research is to test the hypothesis that CD4+ T cell autonomous ER and TNFR2 signaling contributes to AhR-dependent Treg differentiation and function. The following three innovative aims will be tested to determine the impact of ER and TNFR2 signaling on the decision of a CD4+ T cell to differentiate into a Treg in response to AhR activation. Aim 1 will identify the role of ER in AhR ligand-induced Treg differentiation and function and is expected to describe a better understanding of how estrogenic compounds may impact AhR-based immune therapies aimed to induce Treg development. Aim 2 will establish whether selective estrogen receptor modulators (SERMs) utilize AhR to induce Treg differentiation and function and is expected to positively impact the development of effective SERM-based autoimmune therapy. Aim 3 will determine the role of TNFR2 in AhR- induced Treg differentiation and function and is expected to significantly improve our understanding of sex-biased autoimmune disease susceptibility and treatment. Successful completion of the proposed studies should result in the significant, original contribution of advancing autoimmune disease prevention and treatment by targeting AhR-induced Treg differentiation.